Nice work Spomenko, I like your decapper. I don’t completely understand how the light bulbs are being applied though. Sounds like maybe they’re being used as a current limiting device. I'm also not clear what you're using for a power source: AC line voltage or a DC source like a 12V battery?

TommyT, if you put enough current through any metal it will get hot. All metals have some resistance, even copper. The amount of heat a metal will generate is given by P = I*I*R. If current is in amps and resistance is in ohms, the power output will be in watts. You really don’t want to use a good conductor of electricity (low R) in this application since the equation (P=I*I*R) would then require huge amount of current to make heat. A more ideal metal (or metal alloy) is one that has a moderate resistance so you can use less current to get the heating power you want.

Most of your household electrical devices (toasters, ovens, stoves, hair driers, coffee pot, etc) use a Nickel Chromium metal alloy for heating. This alloy has a moderate resistance and retains good mechanical properties even at very high (red hot) temps. http://en.wikipedia.org/wiki/Nichrome

This application is probably using mild steel for metal. Steel and iron are not great conductors of electricity and hence they heat up a lot faster than copper.

Another option for a 12volt DC power source would be a computer power supply. They can typically supply at least 350watts on the 12volt rails. That’s enough watts to make some serious heat. The 12volt rail is used to power the main CPU (and Video cards) in PCs and CPU these days can suck down 125watts when maxed out.

In my country where I live and work there are a lot of beekeepers that something is missing.Many beekeepers move bees at 100-200 km, and they need the opener on the lawn with only a battery of 12 v.Centrifuge to 12 V and openers and they need to 12 V.That would allow them to then I thought of how to earn and to make such a device.There are many inexpensive to maintain, 8 bulb costs 2.4 evra.Make of steel for the blades of Brent.A lot of them are expensive, 30 euros the whole device.I know what you have listed on the relationship between electric current, voltage, power, resistance, but you do not know the Serbs. (People of the Balkans, and I am one of them, still)That's why this is so.

I do know a pretty smart guy from the Balkens named Zoran, but now he lives in Chicago and he doesn’t keep bees. America was also blessed with a pretty smart electrical guy named Nikola Tesla from your part of the world! We can thank him for AC power.

Like I said, I do like your design, I’m just trying to understand exactly how it works. Now that I know you’re using a battery for power, I think I might understand. Is it wired like this?

I could be wrong, but it looks like he isn't using the bulbs to limit the current. After looking at the pics, it looks like he made a metal channel under the blade to hold the bulbs. The bulbs are providing the heat.

Ahhh, I think you’re right BeeV! Good catch. 168 watts of heat from the light bulbs trapped in a metal channel might do it. We might have a problem with this approach in America due to the new efficiency laws for light bulbs. Maybe that only applies for bulbs over 60Watts, I can’t recall. It would be interesting to replace those bulbs with some NiCr wire from ebay.

I believe Spomenko said his bulbs cost 2.4 euros. The euro is collapsing relative to the dollar, but it’s still worth about 1.26 dollars. I bought 20 feet (6 meters) of 22 gauge NiCr wire on ebay last spring for about $5 (about 4 euros). The NiCr wire might make for a competitive heat source in this application.

You may only need 0.5 meters of NiCr wire for each heater and hence the cost might drop to 0.33 euros (42 cents). You would probably want to run through a little math to match the resistance of the NiCr to your source voltage to tune the system to generate just the right amount of heat. You could also add in a nFET transistor and PWM the voltage to the NiCr to create a variable heat supply, but then you lose some of the simplicity of the original idea.

No problems with the type of heater, everything is permitted.The problem is that here in Serbia, all beekeepers do not have the confidence to new things.Simply the bulbs I wanted them closer to the simplicity of appliances to make it easier to accept.Thus always have the option to repair the heater, the field quickly and easily.Can be used by any type of heaters, but that the temperature does not exceed 40-45 degrees Celsius (104-113 F) because of the quality of honey.The knife is heated only to non Paste wax and honey.

With us the voltage in the 220 V, with you is 120 V, the heater was not important, only the thermostat is required for temperature.